Page:Vitruvius the Ten Books on Architecture.djvu/258

220 for it has not the same shade in all the places where it is found, but is naturally qualified by the course of the sun.

2. That which is found in Pontus and Gaul is black, because those countries are nearest to the north. As one passes on from north to west, it is found of a bluish shade. Due east and west, what is found is of a violet shade. That which is obtained in southern countries is naturally red in quality, and therefore this is found in the island of Rhodes and in other such countries that are nearest to the course of the sun.

3. After the shellfish have been gathered, they are broken up with iron tools, the blows of which drive out the purple fluid like a flood of tears, and then it is prepared by braying it in mortars. It is called "ostrum" because it is taken from the shells of marine shellfish. On account of its saltness, it soon dries up unless it has honey poured over it.

1. colours are also manufactured by dyeing chalk with madder root and with hysginum. Other colours are made from flowers. Thus, when fresco painters wish to imitate Attic yellow ochre, they put dried violets into a vessel of water, and heat them over a fire; then, when the mixture is ready, they pour it onto a linen cloth, and squeeze it out with the hands, catching the water which is now coloured by the violets, in a mortar. Into this they pour chalk and bray it, obtaining the colour of Attic yellow ochre.

2. They make a fine purple colour by treating bilberry in the same way and mixing it with milk. Those who cannot use malachite green on account of its deamess, dye blue with the plant called dyer's weed, and thus obtain a most vivid green. This is called dyer's malachite green. Again, for want of indigo, they dye Selinusian or anularian chalk with woad, which the Greeks call, and make an imitation of indigo.